Solidifying a thin layer of metal on plastic film

ABSTRACT

Thin layers of lead, tin and other low melting metals are solidified on plastic film without destoying the integrity of such film by contacting a rapidly moving plastic film with the molten metal.

United States Patent 1 1 Alfrey, Jr. et a1.

1 1 SOLIDIFYING A THIN LAYER 0F METAL ON PLASTlC FILM [75] Inventors: Turner Alirey, Jr.; Raymond Douglas Behr; Douglas Stewart Chisholm, all of Midland, Mich.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

22 Filed: June 23, 1971 21 App1.No.: 156,122

Related U.S. Application Data [63] Continuation of Ser. No. 818,533, April 23, 1969,

abandoned.

[561 References Cited UNITED STATES PATENTS 3,143,738 8/1964 Bigelow 117/105 X 1451 Aug.7, 1973 2,629,907 3/1953 Hugger 117/5.3 X 3,429,741 2/1969 Moriarty 117/120 X 2,720,076 10/1955 Sachara 117/115 X 2,934,458 4/1960 Budd et a1. 117/115 X 2,972,185 2/1961 Brennan 117/105 X 2,965,513 12/1960 Brennan... 117/105 X 3,055,768 9/1962 Lassiter 117/46 3,086,879 4/1963 Lassiter 117/160 3,181,967 5/1965 Amos et a1 118/419 3,145,119 8/1945 LaForce et a1. 117/114 3,222,195 12/1965 Pearlstein .,117/160 3,462,288 8/1969 Schmidt et a1 117/37 Primary Examiner-Wil1iam D. Martin Assistant Examiner-Sadie L. Childs Attorney-Griswold & Burdick, M. B. Davey and L. E.

Messenans, Jr.

[57] ABSTRACT Thin layers of lead, tin and other low melting metals are solidified on plastic film without destoying the integrity of such film by contacting a rapidly moving plastic film with the molten metal.

3 Claims, 2 Drawing Figures SOLIDIFYING A TIIIN LAYER F METAL 0N PLASTIC FILM This application is a continuation of application Ser. No. 818,533 filed Apr. 23, 1969 which is now abandoncd.

This invention relates to the solidifying of low melting metals on plastic film. More particularly this invention relates to a method whereby a rapidly moving plastic film contacts or kisses" the surface of molten metal without absorbing such heat as would destroy the integrity of the film whereby a thin layer of metal is solidified or frozen" on the plastic film while the film is contacting the molten metal.

In the past metals have been placed on plastic film by coating the film with molten metals which subsequently solidify or freeze. Such processes are difficult to control and cannot be extended to metals with melting points higher than the heat distortion temperature of the plastic film.

In accordance with this invention, plastic film is con.- tinuously brought into contact with molten metal which is slightly above its melting point and the metal is solidified on the film while the film is in contact with the molten metal.

As indicated above, the process in accordance with this invention differs from a simple metal coating process in that in the latter, a layer of molten metal is applied continuously and the layer solidifies after the coated plastic film exits from the supply of the layer of molten metal. The process in accordance with the present invention accomplishes the solidifying or freezing ofa layer of metal on the plastic film while the film contacts the molten metal. Necessarily, as the plastic exits from the supply of molten metal, any molten metal that clings to the solidified metal must be removed. Removal of the undesirable layer of molten metal is accomplished in several ways. It is removed with either a doctor blade, an air knife, or centrifugal force. Large centrifugal forces can be obtained by simply passing the plastic film around a roll having a fairly small diameter as it exits from the supply of molten metal.

The invention is further illustrated by'the following detailed description read in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic view of apparatus with which our novel process may be {practiced wherein the flow of molten metal over a weir is'utilized, and

FIG. 2 is a diagrammatic view of other apparatus designed to effect the advantages of our invention, wherein a series of rolls are used for bringing the plastic film into contact with the molten metal.

Looking now with more particularity at the drawings, in FIG. 1 the apparatus has been generally designated as wherein tank I contains a supply of molten metal 2 which is heated by means not shown and which is circulated over a generally centrally located weir 5 by means of pump 4 which pumps the molten metal through pipe 3 in the direction shown by the arrows. Plastic film 7 travelling at a high rate of speed around roller 6 contacts the'surface of the metal as it flows over weir 5. Doctor blade 11 removes any molten metal that clings to the solidified metal as the plastic exits from the supply of molten metal. An inert gas envelopes the surface of the molten metal. The supply of the molten metal can be maintained in a variety of ways (not shown). Inert gas 12 is fed, by means not shown, into the system to replace that lost to the atmosphere.

In FIG. 2, the apparatus used to practice the novel process is generally designated by reference numeral 30. Tank 13 carries a contacted of moltem metal 14., the surface of which is contact by plastic film 15 travelling at a high rate of speed from large roll 17- to smaller roll 16 and thence upward to nip rolls 18 and 19. Doctor blade 20 is used to remove any molten metal that might be clinging to the solidified metal. A supply of molten metal is kept up to the desired level by means not shown.

A variety of apparatus designs are available for bringing the plastic film into contact with the molten metal. The film travelling around a roll can, as in FIG. 1, contact the curved surface of the metal as it flows over a weir; the film travelling around a roll can kiss" the surface of a pool of metal as shown in FIG. 2; the film travelling around a roll can contact a meniscus of metal which forms at a narrow passageway or slit when the metal is subjected to a slight pressure head; or it can contact a fountain of metal that exits from a narrow passage when the metal is subjected to a pressure head sufficient to produce flow. If desired, an apparatus such as that shown in U.S. Pat. No. 3,429,741 may be employed withadvantage. In each of these cases the plastic film could travel around a curved surface rather than a roll and in some cases it could travel over a flat surface. However, from the standpoint of obtaining a narrow contact and therefore short contact time, a small radius of curvature is desirable.

All of the above apparatus is designed to perform in accordance with theinvention, and to do that the molten metal must contact the film for a very short time. In order for this to happen the film must travel at a very high speed and/or the film must contact the molten metal for a very short distance in order that the contact time is such that the heat from the metal does not destroy the plastic film. Desirably, the contact time is less than 10 seconds, and advantageously is ID" seconds or less. At these contact times the surface of the plastic is melted sufficiently to increase the adhesion of the plastic to the metal, but the film is not destroyed.

By low melting metal" is meant any metal or alloy which melts below 400 C. These include, for example, selenium, thallium, bismuth, lead, tin and cadmium and binary, ternary, quaternary and quinary mixtures of such metals with one or more metals such as indium, zinc, silver and antimony.

Utilizing the apparatus shown in FIG. 1, tin is solidified on a 2 mil thick film of polyethylene. The roll 6 is one-half the diameter of the drive roll (not shown).

Tin is heated in tank 1 of the apparatus shown in FIG. 1 to232 C. and maintained at such temperature while being pumped to flow over the weir. Argon is pumped in and maintained over the surface of the molten tin within the tank to prevent oxidation. Roll 6 is adjusted so that the polyethylene film travelling over it just contacts the molten metal as it curves away from the weir 5. Doctor blade 11 isadjusted to remove any molten metal that might cling to the solidified metal. This adjustment is set at 0.2 mil from the film surface. The film speed is b 2,500 feet per minute and the contact time is 10 seconds. The film is put into motion and at the desired speed, roll 6 is lowered so that the 32 C. film kisses the 232C. metal. Two hundred feet of film are run off and upon examination, the film is shown to have an even coating of solidified tin on the order of 0.2 mil thick.

It is to be understood that the example given herein is illustrative rather than restrictive Other metals and alloys thereof such as, for example, lead, bismuth, cadmium and the like, as well as other film substrates such as, for example, Mylar, polypropylene, and the like may also be employed with equivalent results.

We claim:

1. In the process of continuously applying a thin layer of metal having a melting point below 400C, which solidifies on polyethylene film having a melting point below that of the metal, the improvement which comprises circulating the molten metal over a weir and moving the polyethylene film by roller means to effect a kissing contact of the film with the surface of the metal as it curves over said weir, thereby effecting a momentary contact of less than 10 second of a surface of the poyethylene film with the surface of the metal while the metal is slightly above its melting point whereby the metal is solidified on said film while the film is in contact with the molten metal.

2. Process of claim 1 wherein the thin layer of metal is 0.2 mil thick tin and the plastic film is 2 mil thick polyethylene.

3. Process of claim 1 wherein excess molten metal is removed from the solidified layer of metal following the contact of the surface of the metal and the film. 

2. Process of claim 1 wherein the thin layer of metal is 0.2 mil thick tin and the plastic film is 2 mil thick polyethylene.
 3. Process of claim 1 wherein excess molten metal is removed from the solidified layer of metal following the contact of the surface of the metal and the film. 